This invention relates generally to an actuator for rotating a shaft and particularly to a valve actuator for rotating the stem of a cut-off valve.
Rotary valves are used in a wide variety of fluid flow control systems ranging from gas control systems to liquid herbicide spray control systems. It is frequently necessary to actuate such valves remotely and typically this is achieved by the use of hydraulic actuators. Several devices of this kind exist in the prior art but in general they appear to be either complicated, expensive or both and there is a need for an effective simple and inexpensive valve actuator of this type.
Several of the known actuators utilize a hydraulically actuated piston mechanically connected to the valve stem. One device, described in U.S. Pat. No. 4,034,958, provides a rack and pinion type of connection between the piston and valve stem and requires a sequential venting and damping system. Another, earlier device, disclosed in U.S. Pat. No. 1,067,414 provides a valve actuator arm connected to the valve stem and operated by a sliding piston which is slotted to receive the arm. The former device is relatively complicated mechanically and the latter suffers from the inherent disadvantage of having a significant amount of play between the moving parts during reversal action.
The present device overcomes these and other disadvantages in a manner not disclosed in the known prior art.